docs: document all error message types in checkpatch

    However this is not always the case (See signal.h).

    This message type is emitted only for includes from arch/.

  **ARRAY_SIZE**

    The ARRAY_SIZE(foo) macro should be preferred over

    sizeof(foo)/sizeof(foo[0]) for finding number of elements in an

    array.

    The macro is defined in include/linux/kernel.h::

      #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))

  **AVOID_BUG**

    BUG() or BUG_ON() should be avoided totally.

    Use WARN() and WARN_ON() instead, and handle the "impossible"

    error condition as gracefully as possible.

    See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on

  **AVOID_EXTERNS**

    Function prototypes don't need to be declared extern in .h

    files.  It's assumed by the compiler and is unnecessary.

  **AVOID_L_PREFIX**

    Local symbol names that are prefixed with `.L` should be avoided,

    as this has special meaning for the assembler; a symbol entry will

    not be emitted into the symbol table.  This can prevent `objtool`

    from generating correct unwind info.

    Symbols with STB_LOCAL binding may still be used, and `.L` prefixed

    local symbol names are still generally usable within a function,

    but `.L` prefixed local symbol names should not be used to denote

    the beginning or end of code regions via

    `SYM_CODE_START_LOCAL`/`SYM_CODE_END`

  **BIT_MACRO**

    Defines like: 1 << <digit> could be BIT(digit).

    The BIT() macro is defined in include/linux/bitops.h::

      #define BIT(nr)         (1UL << (nr))

  **CONSIDER_KSTRTO**

    The simple_strtol(), simple_strtoll(), simple_strtoul(), and

    simple_strtoull() functions explicitly ignore overflows, which

    correct replacements.

    See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull

  **LOCKDEP**

    The lockdep_no_validate class was added as a temporary measure to

    prevent warnings on conversion of device->sem to device->mutex.

    It should not be used for any other purpose.

    See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/

  **MALFORMED_INCLUDE**

    The #include statement has a malformed path.  This has happened

    because the author has included a double slash "//" in the pathname

    accidentally.

  **USE_LOCKDEP**

    lockdep_assert_held() annotations should be preferred over

    assertions based on spin_is_locked()

    See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations

  **UAPI_INCLUDE**

    No #include statements in include/uapi should use a uapi/ path.

Comment style

-------------

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting

Commit message

--------------

    source patch.

    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin

  **DIFF_IN_COMMIT_MSG**

    Avoid having diff content in commit message.

    This causes problems when one tries to apply a file containing both

    the changelog and the diff because patch(1) tries to apply the diff

    which it found in the changelog.

    See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/

  **GERRIT_CHANGE_ID**

    To be picked up by gerrit, the footer of the commit message might

    have a Change-Id like::

      Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b

      Signed-off-by: A. U. Thor <author@example.com>

    The Change-Id line must be removed before submitting.

  **GIT_COMMIT_ID**

    The proper way to reference a commit id is:

    commit <12+ chars of sha1> ("<title line>")

    An example may be::

      Commit e21d2170f36602ae2708 ("video: remove unnecessary

      platform_set_drvdata()") removed the unnecessary

      platform_set_drvdata(), but left the variable "dev" unused,

      delete it.

    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes

Comparison style

----------------

    side of the test should be avoided.

Macros, Attributes and Symbols

------------------------------

  **ARRAY_SIZE**

    The ARRAY_SIZE(foo) macro should be preferred over

    sizeof(foo)/sizeof(foo[0]) for finding number of elements in an

    array.

    The macro is defined in include/linux/kernel.h::

      #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))

  **AVOID_EXTERNS**

    Function prototypes don't need to be declared extern in .h

    files.  It's assumed by the compiler and is unnecessary.

  **AVOID_L_PREFIX**

    Local symbol names that are prefixed with `.L` should be avoided,

    as this has special meaning for the assembler; a symbol entry will

    not be emitted into the symbol table.  This can prevent `objtool`

    from generating correct unwind info.

    Symbols with STB_LOCAL binding may still be used, and `.L` prefixed

    local symbol names are still generally usable within a function,

    but `.L` prefixed local symbol names should not be used to denote

    the beginning or end of code regions via

    `SYM_CODE_START_LOCAL`/`SYM_CODE_END`

  **BIT_MACRO**

    Defines like: 1 << <digit> could be BIT(digit).

    The BIT() macro is defined in include/linux/bitops.h::

      #define BIT(nr)         (1UL << (nr))

  **CONST_READ_MOSTLY**

    When a variable is tagged with the __read_mostly annotation, it is a

    signal to the compiler that accesses to the variable will be mostly

    reads and rarely(but NOT never) a write.

    const __read_mostly does not make any sense as const data is already

    read-only.  The __read_mostly annotation thus should be removed.

  **DATE_TIME**

    It is generally desirable that building the same source code with

    the same set of tools is reproducible, i.e. the output is always

    exactly the same.

    The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,

    and enables warnings if they are used as they can lead to

    non-deterministic builds.

    See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps

  **DEFINE_ARCH_HAS**

    The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong.

    For big conceptual features use Kconfig symbols instead.  And for

    smaller things where we have compatibility fallback functions but

    want architectures able to override them with optimized ones, we

    should either use weak functions (appropriate for some cases), or

    the symbol that protects them should be the same symbol we use.

    See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/

  **INIT_ATTRIBUTE**

    Const init definitions should use __initconst instead of

    __initdata.

    Similarly init definitions without const require a separate

    use of const.

  **INLINE_LOCATION**

    The inline keyword should sit between storage class and type.

    For example, the following segment::

      inline static int example_function(void)

      {

              ...

      }

    should be::

      static inline int example_function(void)

      {

              ...

      }

  **MULTISTATEMENT_MACRO_USE_DO_WHILE**

    Macros with multiple statements should be enclosed in a

    do - while block.  Same should also be the case for macros

    starting with `if` to avoid logic defects::

      #define macrofun(a, b, c)                 \

        do {                                    \

                if (a == 5)                     \

                        do_this(b, c);          \

        } while (0)

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl

  **WEAK_DECLARATION**

    Using weak declarations like __attribute__((weak)) or __weak

    can have unintended link defects.  Avoid using them.

Functions and Variables

-----------------------

  **CAMELCASE**

    Avoid CamelCase Identifiers.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming

  **FUNCTION_WITHOUT_ARGS**

    Function declarations without arguments like::

      int foo()

    should be::

      int foo(void)

  **GLOBAL_INITIALISERS**

    Global variables should not be initialized explicitly to

    0 (or NULL, false, etc.).  Your compiler (or rather your

    loader, which is responsible for zeroing out the relevant

    sections) automatically does it for you.

  **INITIALISED_STATIC**

    Static variables should not be initialized explicitly to zero.

    Your compiler (or rather your loader) automatically does

    it for you.

  **RETURN_PARENTHESES**

    return is not a function and as such doesn't need parentheses::

      return (bar);

    can simply be::

      return bar;

Spacing and Brackets

--------------------

      printk(KERN_INFO "bar");

  **ELSE_AFTER_BRACE**

    `else {` should follow the closing block `}` on the same line.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces

  **LINE_SPACING**

    Vertical space is wasted given the limited number of lines an

    editor window can display when multiple blank lines are used.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces

  **OPEN_BRACE**

    The opening brace should be following the function definitions on the

    next line.  For any non-functional block it should be on the same line

    as the last construct.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces

  **POINTER_LOCATION**

    When using pointer data or a function that returns a pointer type,

    the preferred use of * is adjacent to the data name or function name

    and not adjacent to the type name.

    Examples::

      char *linux_banner;

      unsigned long long memparse(char *ptr, char **retptr);

      char *match_strdup(substring_t *s);

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces

  **SPACING**

    Whitespace style used in the kernel sources is described in kernel docs.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces

  **SWITCH_CASE_INDENT_LEVEL**

    switch should be at the same indent as case.

    Example::

      switch (suffix) {

      case 'G':

      case 'g':

              mem <<= 30;

              break;

      case 'M':

      case 'm':

              mem <<= 20;

              break;

      case 'K':

      case 'k':

              mem <<= 10;

              /* fall through */

      default:

              break;

      }

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation

  **TRAILING_WHITESPACE**

    Trailing whitespace should always be removed.

    Some editors highlight the trailing whitespace and cause visual

    distractions when editing files.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces

  **WHILE_AFTER_BRACE**

    while should follow the closing bracket on the same line::

      do {

              ...

      } while(something);

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces

Others

------

  **CAMELCASE**

    Avoid CamelCase Identifiers.

    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming

  **CONFIG_DESCRIPTION**

    Kconfig symbols should have a help text which fully describes

    it.

  **CORRUPTED_PATCH**

    The patch seems to be corrupted or lines are wrapped.

    Please regenerate the patch file before sending it to the maintainer.

  **DOS_LINE_ENDINGS**

    For DOS-formatted patches, there are extra ^M symbols at the end of

    the line.  These should be removed.

  **EXECUTE_PERMISSIONS**

    There is no reason for source files to be executable.  The executable

    bit can be removed safely.

  **NON_OCTAL_PERMISSIONS**

    Permission bits should use 4 digit octal permissions (like 0700 or 0444).

    Avoid using any other base like decimal.

  **NOT_UNIFIED_DIFF**

    The patch file does not appear to be in unified-diff format.  Please

    regenerate the patch file before sending it to the maintainer.

  **PRINTF_0XDECIMAL**

    Prefixing 0x with decimal output is defective and should be corrected.

  **TRAILING_STATEMENTS**

    Trailing statements (for example after any conditional) should be

    on the next line.

    Like::

      if (x == y) break;

    should be::

      if (x == y)

              break;